Field of the invention
The present invention relates to a wireless communication system, and more particularly, to a method of transmitting device-to-device (D2D) data and an apparatus using the method.
Related Art
Long term evolution (LTE) based on 3rd generation partnership project (3GPP) technical specification (TS) release 8 is a promising next-generation mobile communication standard. Recently, LTE-advanced (LTE-A) based on 3GPP TS release 10 supporting multiple carriers is under standardization.
According to a downlink control information (DCI) format 1A-based physical downlink control channel (PDCCH) order of LTE and LTE-A systems, an eNodeB (eNB) allows a user equipment (UE) in an RRC_CONNECTED mode to transition from an out-of-synch mode to an in-sync mode by transmitting a command to transmit buffer data, and the UE in the in-sync mode performs physical random access channel (PRACH) transmission. This is similar to an operation in which the UE transmits buffer data by using an uplink PRACH or a scheduling request (SR). In other words, the PDCCH order implies that the eNB commands the UE to achieve a requirement of the eNB (i.e., eNB-to-UE data transmission using a downlink carrier).
The present invention proposes a method in which the eNB commands a designated UE pair to perform D2D communication through a PDCCH and instructs to exchange information between UEs through an uplink carrier/band. The information exchange between the UEs may be called UE-to-UE or device-to-device (D2D) communication, direct communication, point-to-point (P-to-P) communication, etc. The UE-to-UE communication may decrease a waste of a radio resource and a factor of causing an interference.